Lion Air Pilots Had to Fight Safety Device, Crash Report Finds
(Bloomberg) -- Lion Air pilots were fighting a safety device on their Boeing Co. 737 Max that kept trying to dive the plane as they attempted to diagnose multiple apparent failures on the fatal flight, according to a preliminary report by Indonesian investigators.
The first major report by the National Transportation Safety Committee, set for release Wednesday morning local time, stops short of concluding what caused the Oct. 29 crash that killed 189 people in the sea near Jakarta, according to a person familiar with its contents who wasn’t authorized to speak about it.
It adds new data about maintenance of the jet as well as the airline’s instructions for pilots, Boeing’s flight manuals, the local weather and efforts to recover the wreckage of the almost new aircraft that struck the water at high speed, the person said. The report also contains flight data that were released last week in a briefing with lawmakers showing pilots repeatedly commanding the plane to raise its nose to counteract an automated safety program trying to dive as a result of faulty data.
The pilots of the plane were inundated with safety alerts and flight information that differed between the captain and copilot’s instruments, starting in part even before they took off, according to the plane’s crash-proof data recorder.
A device known as a stick shaker -- a warning that the wings are about to lose lift, which vibrates the control column and also makes a loud thumping noise -- was activated shortly after takeoff for the captain but not the copilot, according to the data. It was apparently triggered by a faulty device measuring angle of attack, or the degree to which the nose of the plane is pointed up or down compared to the onrushing air.
That erroneous sensor was also triggering safety software newly added to the Max. The Maneuvering Characteristics Augmentation System is designed to ensure the wings don’t lose lift, which is known as an aerodynamic stall. It was programmed to automatically lower the nose and was doing so for most of the 11-minute flight even though the plane was not close to stalling.
The pilots were responding by hitting a switch on their control column that temporarily raised the nose, but it only stopped the MCAS temporarily.
The previous flight of the doomed plane experienced the same failure of its angle of attack sensor, raising questions about what repairs were performed before the crash.
Related: Search For Crashed Boeing Jet’s Cockpit Recorder Set to Resume
Boeing earlier this month issued a bulletin to operators of the Max reminding them that such a cascade of failures could be addressed by an existing emergency procedure. The manufacturer has said it’s confident in the safety of the latest version of its 737 model.
Flight data presented to Indonesian lawmakers on Thursday showed that pilots on a flight the previous day on the same plane appear to have followed that procedure, which calls for shutting off the motor that commands so-called pitch trim. The trim system is what MCAS was using to lower the nose.
Indonesian authorities met with families of passengers on Monday in Bangka and Jakarta to provide a snapshot of the preliminary findings. Those who attended the briefing say it didn’t indicate a cause for the crash.
“There was no explanation related to Boeing,” said Ari Priawan, whose brother, sister-in-law and their child were on board Flight JT610.
Investigators say they hope to resume the search for the plane’s voice data recorder when equipment is obtained. A ship that can hold its position in one spot without casting anchor is needed because of the presence of many gas pipelines in the area, said Nurcahyo Utomo, the lead investigator.
“The search for the cockpit voice recorder will resume,” Utomo said. “We are hoping to start this week and will put in our maximum efforts.”
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